Information Technology Reference
In-Depth Information
User B
S
E
R
V
E
R
User A
Resolution
layer n
User C
P slices
Thumbnail
video
C
L
I
E
N
T
S
RoIs of users
User A
User B
User C
Fig. 6
Example illustrating RoIs of three users within the multi-resolution video representa-
tion. The slices shown shaded are commonly wanted by more than one user and represent the
“overlaps” exploited by the IRoI P2P system.
peer subscribes the base layer at all times and additionally some enhancement layer
slices that are required to render the RoI. Peers also dynamically unsubscribe slices
that are no longer required to render the RoI. The RoI prediction lookahead accounts
for the latency in joining new trees as well as the playout delay that is employed to
mitigate delay jitter among the high-resolution slice packets.
5.2
P2P Protocol
The server maintains a database of slices that each peer is currently subscribed to.
Whenever the RoI prediction indicates a change of RoI, the peer sends an RoI-switch
request to the server. This consists of the top-left and bottom-right slice IDs of the
old RoI as well as the new RoI. In response to the RoI-switch request, the server
sends a list of potential parents for every new multicast tree that the peer needs to
subscribe. Corresponding to every multicast tree, there is a limit on the number of
peers the server can directly serve, and the server includes itself in the list if this
quota is not yet full. The server also updates its database assuming that the peer will
be successful in updating its subscriptions. After receiving the list from the server,
the peer probes potential parents for every new multicast tree it needs to join. If
it receives a positive reply, it sends an attach request for that tree. If it still fails
to connect, the peer checks for positive replies from other probed peers and tries
attaching to one of them. Once connected to any multicast tree corresponding to a
slice, the peer checks if it has previously received the corresponding background I
slice. If it has not then the peer obtains the background I slice from one of the peers
in the list or the server.
